What matters should be paid attention to when medical device products are treated with sandblasting machine?

Key points of surface treatment control of medical device sandblasting machine (conforming to ISO13485, biocompatibility, cleanliness, no precipitation, no metal pollution and sterilization adaptation requirements)

Medical devices are different from ordinary workpieces: core control of metal cross-contamination, ion precipitation, burr embedding, controllable roughness, no residual abrasive, hydrogen embrittlement, biocompatibility, cleanliness and dust-free, sterilization tolerance, and are divided into seven modules: equipment, abrasive, workpiece protection, process, before and after cleaning, inspection and workshop management.

A, sandblasting machine equipment specialized transformation (clean medical grade hard requirements)

Special plane, it is forbidden to mix materials.

Stainless steel 316L, titanium alloy, plastic/PEEK, aluminum alloy and polymer fittings must be sandblasted; One equipment only deals with a single material to prevent carbon steel and iron filings from being embedded in the workpiece to cause electrochemical corrosion, rust and precipitation of heavy metals.

The cavity, inner container, recycling hopper, spray gun, mesh belt conveyor and turntable are all made of 304/316 stainless steel; It is forbidden to use ordinary carbon steel inner walls and iron screws, so as to avoid the products from being polluted by rusted iron powder.

Mandatory configuration of abrasive recovery and purification system

Cyclone separation+multilayer screening+magnetic separation device; Removing free iron impurities by magnetic separation, and separating and crushing fine sand and dust by a screen; If the proportion of broken abrasives exceeds 10%, all of them should be replaced. Fine powder is easy to get stuck in micropores and gaps, and it is difficult to clean.

The dust removal filter element filters efficiently to prevent the dust from spreading to the clean workshop, and the pressure difference is monitored regularly to prevent the dust from blowing back and polluting the workpiece.

Oil-free and waterless aseptic treatment of gas source

The compressed air pipeline is all stainless steel, equipped with freeze dryer+three-stage oil removal filter+activated carbon filtration, with dew point ≤-40℃, no oil, no moisture and no hydrocarbon precipitation;

The air storage tank and pipeline discharge pollutants every day, and the water vapor will cause the abrasive to be caked with moisture, the surface of the workpiece to be stained with water, and spot corrosion will occur after later sterilization.

Sealing and dustproof of automation equipment

Automatic translation/rotary disk sandblasting machine is fully enclosed, and the door body is sealed with silica gel to prevent sandblasting dust from leaking and polluting the 10,000-class/100,000-class clean workshop; The bottom of the equipment is provided with a dust collection tank, which is thoroughly cleaned in each shift.

Wear-resistant ceramic nozzles are selected for nozzles, which should be replaced immediately after wear, so as to avoid local overspray and excessive roughness caused by uneven pressure.

Anti-static design

Catheters, plastics and silica gel medical devices are easy to adsorb dust electrostatically, and the equipment is reliably grounded, and the grounding resistance is ≤ 4Ω; Control the humidity in the workshop by 45%–60% to reduce electrostatic dust.

Second, abrasive selection and control (biocompatibility core)

1. Different medical device substrates match abrasives.

form

Workpiece materials are compliant. Abrasive is strictly prohibited. Control purposes

316L medical stainless steel, titanium alloy implants (bone nails, joints, implant brackets), high-purity white corundum, ceramic sand, medical glass bead carbon steel pills, brown corundum, iron-containing abrasives, prevent iron impurities from being embedded, and avoid human metal ion precipitation and allergy.

PEEK, PC, ABS plastic instruments, injection-molded plastic beads, fine glass beads, high-hardness alumina, and metal sand prevent the substrate from scratching, whitening, cracking and surface pulverization.

Aluminum alloy instrument shell, surgical instrument handle glass beads, stainless steel pellets and ordinary iron sand prevent iron pollution and ensure anodic oxidation adhesion.

Silica gel, soft medical accessories, very fine food-grade plastic sand, and low-pressure micro-spraying hard abrasive to avoid surface damage and debris falling off.

2. Abrasive incoming and circulation control

Inspection report shall be provided when entering the factory: heavy metal content is up to standard, chloride ion is low, there is no sulfide and soluble salt; Abrasive shall not contain excessive silicon dust (to avoid silicosis of operators+silicon residue of workpieces).

The new abrasive is screened, cleaned with pure water and dried before being put into use to remove production dust and salt.

Different abrasives are stored in sealed zones, which are moisture-proof and dust-proof, with clear marks and no mixing; The circulating abrasive shall be screened in each shift to eliminate metal chips and broken sand.

Implantable high-risk products suggest disposable abrasives, which are not recycled to completely eliminate cross-contamination.

3. Workpiece pretreatment and shielding tooling before sandblasting

Completely degrease and remove oil.

Firstly, the workpiece is washed by ultrasonic alkali → rinsed by pure water → dried; The oil stain will stick to the embedded gap of abrasive particles, which can not be removed after subsequent cleaning. After high-temperature sterilization, foreign bodies will be precipitated and black spots will be produced.

It is forbidden to touch the sandblasting surface of the workpiece directly. Grease fingerprints will cause uneven sandblasting and local pollution.

Precision feature full shielding protection

Thread, sealing surface, mirror polishing area, inner hole of catheter, mating dimension surface and sealing ring groove are covered with medical silicone plug and stainless steel cover plate;

Ordinary masking paper and ordinary adhesive tape are prohibited, and the adhesive will remain after sandblasting impact, and harmful substances will be precipitated from the residual adhesive after ethylene oxide sterilization, which will affect biocompatibility.

Special tooling for thin-walled and slender parts

Puncture needles, thin implants and small surgical pieces adopt multi-point hollow tooling to ensure full coverage sandblasting without shielding; Control the removal amount of single-sided material ≤0.015mm to prevent deformation and size out of tolerance.

The tooling material is homogeneous with the workpiece, and the surface sand is cleaned regularly to avoid secondary pollution.

Four, sand blasting process parameters control (roughness, surface stress, appearance stability)

Pressure grading control

Implanting titanium alloy/stainless steel precision parts: 0.15-0.3MPa low-pressure micro-spray, to prevent micro-cracks on the surface and reduce the risk of metal ion precipitation;

Roughening of stainless steel (increasing coating adhesion): 0.3–0.4 MPa;

Plastic/soft material: ≤0.2MPa, extremely low pressure, to prevent matrix damage.

Specification for spray gun attitude

The injection angle is 40 ~ 60, and 90 vertical strong impact is prohibited; The spraying distance is 120–180 mm, the walking speed of automatic equipment is fixed, and the program encryption cannot be modified at will.

Strictly control the three hazards of overspray

(1) the workpiece wall thickness thinning, size tolerance; (2) tiny pits are generated on the surface layer, which is easy to hide dirt and accept dirt, and bacteria remain after sterilization; ③ The roughness Ra is too large, which increases the absorption of body fluids, and the implant is prone to produce inflammatory reaction.

The drawings stipulate that the roughness should be strictly locked for the process time, and it is not allowed to artificially extend the sandblasting time.

Hydrogen embrittlement prevention of high strength stainless steel workpiece

Stainless steel implants with tensile strength > ＞1100MPa can avoid long-term dry sandblasting; After sandblasting, remove hydrogen and bake according to specifications to prevent hydrogen brittle fracture during use.

V. Cleaning and cleaning after sandblasting (the most important thing for medical devices)

Clean the whole process immediately after leaving the machine, so as to eliminate the embedded residue of abrasive (FOD foreign body risk);

Clean compressed air sweeping → pure water ultrasonic cleaning → high purity purified water rinsing → dust-free hot air drying;

Blind holes, deep threads, and small catheter lumens were flushed with pulsed high pressure, and no sand residue was found by naked eye and microscope inspection.

Mandatory items for cleanliness testing

Water bursting test: the surface is free of oil stains and particles;

Ion detection: the content of chloride ion and soluble salt on the surface is up to standard;

Metallographic/magnifying glass inspection: no embedded iron chips and abrasive particles;

Wipe test: Dust-free cloth wipes without dust and impurities of different colors.

Transshipment and storage requirements

Immediately after drying, it is transferred to a clean area and sealed and packaged with a dust-free PP bag; Wear powder-free and dust-free gloves all the time, and it is forbidden to touch the sandblasting surface with bare hands;

After sandblasting, finish post-treatment such as anodizing, passivation, spraying and polishing within 24 hours to avoid surface oxidation and dust accumulation.

Six, the workshop environment, personnel and system traceability (ISO13485 requirements)

The sand blasting process is separated from the clean area of injection molding, machining and assembly, and independent dust removal is set to prevent dust from floating into the clean area of finished products; Epoxy antistatic floor, vacuuming and mopping the floor every day.

Personal protection: air-supplied dust mask, anti-static dust-free sandblasting suit, powder-free rubber gloves; It is forbidden for cotton yarn and ordinary brush to enter the operation area, and cotton yarn fiber is easy to leave gaps in the workpiece.

Complete batch traceability record (retained for at least 10 years)

Records of each batch: product drawing number, batch number, abrasive model, sandblasting pressure, walking speed, sandblasting time, roughness detection, cleaning records, equipment spot inspection and operators; Automatic sandblasting machine saves process parameter log.

Daily equipment inspection list

Gas source oil-water separation, nozzle wear, iron impurity content in magnetic separation, screen crushing rate, dust removal pressure difference, cavity cleanliness, grounding resistance.

Seven, different categories of medical devices exclusive taboo

Implantable products (bone nails, artificial joints, vascular stents)

No circulating abrasive; No iron pollution in the whole process; Strengthen passivation treatment after sandblasting; Strictly control roughness to avoid metal precipitation and tissue stimulation in the body; Biocompatibility must be verified.

Surgical instruments (scalpel, hemostatic forceps, endoscope accessories)

Only slightly matte finish, no overspray; The cutting edge and occlusal surface are completely covered; Passivation and rust prevention after sandblasting can meet the requirements of repeated sterilization at high temperature and high pressure without rust.

Plastic/PEEK medical consumables shell

Sand blasting at low pressure for a short time, and hard abrasives are prohibited; Prevent the surface from cracking and whitening, and avoid accelerating aging and precipitating plasticizer after soaking in disinfectant.

Minimally invasive catheter, micro-channel valve body

All inner holes are blocked; After sandblasting, high-pressure flushing is carried out to prevent sand particles from blocking the pipeline and causing foreign body risks in clinical use.

Stainless steel infusion stand, medical equipment shell

Ceramic sand can be recycled, but it can be treated by a separate unit; Controlling roughness is convenient for daily alcohol wiping and disinfection, and it is not easy to hide bacteria.

VIII. Summary of Common Quality Risk Avoidance

Iron impurity embedding → carbon steel fittings, mixing materials and abrasives of equipment are not magnetically separated → products rust, metal precipitation and medical adverse reactions;

Abrasive remains in the inner cavity → the cleaning process is simplified, and the small pores are not washed → clinical foreign body accidents;

Oil stain is not removed completely → black spots after sandblasting, and harmful substances are separated out after sterilization;

Overjet roughness exceeds the standard → easy to hide bacteria and the risk of implant inflammation;

The gas source contains water and oil → the workpiece is corroded by water and the coating falls off;

Masking residual glue with adhesive tape → sterilizing with ethylene oxide to separate out toxic substances;

Different materials share a sandblasting machine → cross-contamination, batch scrapping.