塑膠熔接機之超音波暴露防護

Control of Ultrasound Exposure from Plastic Welding Machine

林宛宜(Wan-Yi Lin)

指導教授 ： 黃耀輝

國立臺灣大學/公共衛生學院/公共衛生碩士學位學程/碩士(2022年)

https://doi.org/10.6342/NTU202200157

摘要

人耳的聽覺範圍為 16 kHz-20k Hz，高於這個範圍就稱為超音波，其頻率高、波長短且具方向性，在傳播時能量會因被介質吸收而衰減。多數產品為了兼顧產品的美觀及防水性能，於組裝過程中會使用超音波塑膠熔接機將產品進行熔接。這類塑膠熔接機的熔接頻率約為20 kHz，幾近超出人耳可聽到的頻率範圍（20 Hz~20 kHz）。
眾多研究顯示人體長時間處於高音量的超音波環境下，可能會導致耳鳴、心悸、頭昏、噁心等症狀，甚至可能發生聽力損傷。本實務實習之塑膠熔接機作業場所已有部分操作人員反映不適感，故期能藉由此機會，進行塑膠熔接機之超音波暴露探討，並試著提出有效消除或控制此暴露之措施。
本研究使用Svan 912AE（Type 1 Sound Level Meter）噪音計在模擬之操作人員實際作業位置（約距離機器1 m，距地面1 m處）進行超音波量測，同時採用波蘭中央勞動保護研究所於2019年發表的超音波8小時暴露限值作為改善的判斷。並依據量測所得超音波暴露頻率特性，進行文獻探討及選擇適當的防護材料進行工程改善。完成改善工程後再使用同一部噪音計進行超音波暴露量測，以了解工程措施對於改善超音波暴露的成效。
量測工程改善前操作人員於塑膠熔接機的超音波暴露，初步結果顯示在中心頻率為20 kHz之1/3八音度頻帶量測到的均能音量為93.3 dB，已超過波蘭所建議的職業暴露限值。經探討超音波防治相關文獻後，考量到隔音效果、重量及成本等因素，本實務實習案規劃使用3 mm鋁板進行隔音罩製作，來達到降低操作人員暴露於超音波之目的。
結果顯示，裝設鋁製隔音罩之後的塑膠熔接機作業時發出的超音波，在中心頻率為20 kHz之1/3八音度頻帶量測到的均能音量為76.5 dB，顯示工程改善後的超音波暴露均能音量已低於波蘭所建議的職業暴露限值中一般人員、妊娠婦女和青少年的超音波容許暴露標準。

關鍵字

特徵頻率 ； 超音波暴露 ； 塑膠熔接 ； 職業暴露限值 ； 職業安全衛生

並列摘要

Ultrasound is defined as the sound with frequency higher than the audible sound frequency of 16 kHz~20 kHz, and characterized with high frequency, short wavelength, directional, and energy loss through transmission medium. Ultrasonic plastic welding machine is widely used in the plastic welding assembly process to keep the final product good looking and waterproof. The applied welding frequency is about 20 kHz, which is just beyond the audible sound frequency of 20 Hz~20 kHz for human beings.
Many studies have shown that long-term exposure to high dose ultrasound may cause symptoms such as tinnitus, palpitations, dizziness, nausea, and even hearing loss. Some operators in the study place have complained discomfort, so this study was conducted to explore the ultrasound exposure levels from the plastic welding machine and then propose effective measures to eliminate or control this exposure.
This study applied Svan 912AE (Type 1 Sound Level Meter) noise dosimeter to monitor ultrasound exposure of the operator (approximately 1 m from the machine at 1 m in height). The Interim Guidelines of 8-hour occupational exposure limit for ultrasound, proposed by the National Research Institute of the Poland Central Institute for Labor Protection in 2019, was used for reference. Based on the monitored ultrasound frequency, literature review was conducted accordingly and appropriate protective materials were chosen to reduce the ultrasound exposure level. Then the reduction effectiveness was evaluated through before-and-after comparison for ultrasound exposure levels.
Results of the 1/3 octave band ultrasound measurement show that, the ultrasound level of center frequency 20 kHz was 93.3 dB, exceeding the occupational exposure limit recommended by Poland. After considering sound absorption effectiveness, weight and cost of soundproof cover through literature review, aluminum sheet of 3 mm thick was used to isolate the ultrasound source in order to lower operators’ ultrasound exposure level.
Once the aluminum soundproof cover was installed, the operators’ ultrasound exposure level of 1/3 octave band with center frequency of 20 kHz was reduced to 76.5 dB, within the occupational exposure limit of ultrasound recommended by Poland for workers, pregnant women and juveniles.

並列關鍵字

Characteristic frequency ； Ultrasound exposure ； Plastic welding ； Occupational exposure limits ； Occupational health and safety

參考文獻

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