Fourth, quality inspection methods
Qualified coating surface is smooth, no cracks, dirt and flaws, uniform color, no scorch, nail marks do not leave traces, corner scraping with fingernails will not bulge and peeling, and then can not be cut with a knife Break into it.
Polyvinyl fluoride coatings have excellent anti-corrosion properties, and currently there are more than 100 types of chemical products that can be tested. Due to the different materials used by the barrel manufacturers, such as surface treatment, spraying, and baking, PVF coating has an impact. Therefore, we believe that it is necessary to carry out costume tests on the products that are being packed before and regularly for each new product, and strive to eliminate the hidden dangers of the products in the factory.
1, anti-corrosion coating also through the pinhole inspection to avoid the existence of pinholes and reduce the anti-corrosion effect. The pinhole test method is as follows:
a, 5% copper sulfate solution soaked at room temperature for more than 24 hours, the surface of copper precipitation that there is a pinhole.
b. A 1000-volt hand pendulum megohmmeter, with one pole in contact with the metal of the workpiece, one pen followed by a salt water brush moving over the surface of the coating. When the pointer bounces, it indicates that there is a pinhole in the part. It can also be replaced with a 1.5-volt dry cell with a sensitive galvanometer or microammeter.
c. Pinhole testing equipment can be purchased directly from the market, such as EDM pinhole testing equipment.
2. Adhesion check (cross-cut method) The paint film is to cut 6 parallel scratches with a distance of 10 to 20 cm and a pitch of 1 mm, and then turn it through 90° to form a square grid with the same method. Adhesion of PVF coatings is required to be Class I or higher. Specifically refer to the national standard GB325-91.
V. Common defects
1, common quality problems and treatment methods: (see the following table)
Common defects and improvement methods
unpleasant sight
cause
Improve methods
Peel, wavy
(1) Gun air flow is too fast
(2) spray gun too *close
(3) A spray is too thick
(1) reduce the pressure
(2) Open the distance and keep the muzzle moving
(3) Spraying more
Honeycomb round pit
(4) The primer is decomposed or not dried
(5) Rapid solvent evaporation
(4) Switch to PVF coating
(5) Diluted with dimethyl ester instead of low boiling point solvent
Coking
(6) decomposition caused by excessive temperature
(7) Overdone
(8) Decomposition caused by old paint or original charcoal
(6) Properly lower furnace temperature to facilitate control
(7) timely release
(8) Completely go to the net in advance and hang on the net to go to the net
Soft membrane
(9) There is residual solvent
(10) It is difficult to spray thick evaporation
(9) Extended baking time
(10) Prevent partial multi-spray and flow hanging
Stripping
(11) Residual solvent
(12) Insufficient primer
(13) Surface treatment is not good
(11) Bake more time or raise the temperature
(12) Use PVF primer instead
(13) Ticked off, timely coating after surface treatment
Blank point
(14) oily, water droplets
(14) Rubbing the barrel with alcohol
Pinhole
(15) The coating is too thin
(16) Local Coating Thin
(17) Thin coating at acute corners
(18) The corner is impacted
(15) Recoat once
(16) Partial coating
(17) Pre-sharpened corners to eliminate burrs, etc.
(18) Separated after chilling
Edge crack
(19) The furnace temperature is low
(20) The starting temperature is too low
(21) premature evaporation of the latent solvent
(22) Too many low boiling solvents
(19) Increase furnace temperature
(20) The temperature is not enough to enter the furnace, first close the door to warm up
(21) Stop the blast
(22) Switch to Dimethyl Ester or Diethyl Ester
Cracked, wrinkled
(23) The furnace temperature is too low
(24) The starting temperature is too low
(25) Furnace temperature uneven
(23) Greatly increase the furnace temperature
(24) Turning the temperature up so that the furnace temperature is too high and the furnace moves quickly
(25) Increase thermal power
Color difference
(26) Uneven temperature in the furnace
(27) Large differences in wall thickness
(26) Blow or rotate work
(27) Make thick walls heated more
Coarse grain
(28)Coarse paint
(29) The paint is not even
(28) 180 mesh filter
(29) Stir thoroughly when diluted
2. Repair and retreat of coating:
Unsatisfactory spray quality, rework before baking is much easier, use alcohol or gasoline scrubbing on the line, wait until after baking plastic coating removal is much more difficult. In view of this, try to use the thermoplastic characteristics of the polyvinyl fluoride coating, and take the repair method instead of the removal. However, there are four situations in which retreat should be considered: large areas of scorch, appearance needs to look good, belong to the surface of the mating surface and have been coated repeatedly or repeatedly.
Although there are many types of tapping screws, they all have the following similarities:
(1) are generally made of carbonized carbon steel (accounting for 99% of total production). It can also be made of stainless steel or non-ferrous metals.
(2) The product must be heat treated. Carbon steel tapping screws must be carbonized and stainless steel tapping screws must be solution hardened. In order to make tapping screws to meet the requirements of the standard of mechanical properties and performance.
(3) The product surface hardness is high, the core toughness is good. That is, "soft inside strong outside". This is a major feature of tapping Screw performance requirements. If the surface hardness is low, it can not be screwed into the matrix; If the core toughness is poor, a twist will break, can not be used. So "inside soft outside steel" is self-tapping screw to meet the use of performance, very important requirements.
(4) The surface of the product needs surface protection treatment, generally electroplating treatment. Some product surface must be treated by phosphate (photostatting), such as wall panel self - tapping screws for photostatting.
(5) Production by cold heading process. It is recommended to use high-speed cold heading machine and high-speed wire rolling machine or high-speed planetary wire rolling machine. High speed is emphasized here to ensure product quality. Only the head of tapping screw produced by high-speed machine is well formed and the thread quality is high.
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