Valve castings should have a high strength, stiffness and abrasion resistance, in order to maintain its accuracy is not with the cutting conditions, the use of time and other factors have significant changes, so as to enable the part to be machined with a desirable accuracy and finish. Appropriate choice of materials, heat treatment process and rational structure is the casting performance to meet the requirements. Casting detection process are:
1, eye observation, for obvious defects on castings, such as water shortage, severe surface defects and other cool levels.
2, valve casting dimensions measured, to ensure compliance with the tolerance requirements.
3, metallurgical, chemical, physical and other related casting intrinsic quality testing. Detection means includes: pressure test, in order to determine the casting leak site;-ray detection, magnetic particle inspection, fluoroscopy and ultrasound probe so as to detect the casting surface and internal defects; mechanical testing to determine the mechanical properties of valve castings, such as tensile strength and hardness.
If you detect a defect less serious, the user's consent, you can use welding, grinding or other remedy repair castings.
Casting Process eliminate internal stress, called aging treatment: sub-natural aging, artificial aging and resonance aging.
(1) valve casting natural aging is to cast open place for months, six months or a year or more, so casting Naturally, the deformation occurs slowly, so that the residual stress gradually eliminate themselves. Natural aging cycle length, eliminate internal stress is not complete, for example, be placed only six months to eliminate 30% of residual stress, the current production has been less used. Therefore, often using artificial aging treatment to eliminate casting stress.
(2) resonance aging periodic exciter force - under the exciting force, resonance and casting occur, thus the valve casting obtain considerable vibrational energy. Pay during resonance superimposed alternating stress and residual stress, resulting in local yield, causing the plastic deformation, the casting residual stress relaxation gradually disappeared, so as to achieve the purpose of stable casting size. Dynamic Stress 35MPa approaching when eligible for maximum benefits. General application of dynamic stress 20MPa satisfactory results are obtained. Resonance aging is a time-saving, energy-efficient advanced methods.
(3) artificial aging process is the casting alloy is heated to a plastic state elastic temperature range, at this temperature to maintain a certain time, so that the stress disappear, then slowly cooled to a temperature within the range of elastic deformation, furnace cooling. Artificial aging is usually performed after the rough parts, while eliminating the casting of the original residual stress and eliminates the roughing cutting stress generated in the process. There are also some high precision valve castings, roughing once before artificial aging, rough and then once the artificial aging. |
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